Light-erasable embedded memory device and method of manufacturing the same

ABSTRACT

A light-erasable embedded memory device and a method for manufacturing the same are provided in the present invention. The light-erasable embedded memory device includes a substrate with a memory region and a core circuit region, a floating gate on the memory region of the substrate, at least two light-absorbing films above the floating gate, wherein each light-absorbing film is provided with at least one dummy via hole overlapping the floating gate, and a dielectric layer on each light-absorbing film and filling up the dummy via holes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. application Ser. No. 15/140,506, filed on Apr. 28, 2016, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a memory device and a fabricating method thereof. More particularly, the present invention relates to an illuminating efficiency-increasable and light-erasable embedded memory device and a fabricating method thereof.

2. Description of the Prior Art

A memory is a semiconductor device used for storing data or information. The requirements for memory are becoming higher along with advancements in the function of computer micro-processors and the increase in volume of software programs and calculations. The technique and process for fabricating memory devices with large-volume and low-cost memory are constantly driving the semiconductor technology to go towards high integration.

Among various memory products, a non-volatile memory has been applied widely to personal computers and other electronic equipment in which data can be read from, written to, or erased from the non-volatile memory repeatedly, and data stored in the non-volatile memory will not be lost after power is turned off.

FIG. 1 is a cross-sectional view of a conventional single poly non-volatile memory device.

Referring to FIG. 1, a memory device 102 is disposed on a substrate 100. The memory device 102 includes two metal oxide semiconductor (MOS) transistors 104 and 106 disposed adjacently on the substrate 100. The gates of the MOS transistors 104 and 106 are respectively used as a select gate 108 and a floating gate 110 of the memory device 102. While programming the memory device 102, charges are stored in the floating gate 110. While erasing the data stored in the memory device 102, conventionally, the floating gate 110 is radiated with a UV light so that the charges stored in the floating gate 110 can be erased.

If the memory device 102 is an embedded memory, a metal interconnect structure covers the memory device 102. In a metal interconnect structure adopting a copper process, the metal interconnect is composed of a plurality of copper metal layers formed in a plurality of dielectric layers, and a silicon nitride layer is formed on each dielectric layer as a cap layer for protecting the copper metal layer.

A one-time programmable read-only memory (OTPROM) is a non-volatile memory structure that may be programmed after the memory is manufactured. The OTPROM retains a programmed memory state even when no power is provided to the OTPROM. An OTPROM memory cell array typically includes one bitcell per data bit to be stored. Each row of bitcells in the OTPROM array may be coupled to a signal line known as a wordline. Each column of bitcells in the OTPROM array may be coupled to a signal line known as a bitline.

While the semiconductor device, such as a CMOS, BJT, or diode, is mostly operated by electrical signals, how to integrate the OTPROM process which uses UV light to erase stored electrons in the semiconductor process is still a challenge in the industry.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive overview of the invention. It is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that will be discussed later.

It is a novel concept to forma light permeable passage in the semiconductor device by using existing semiconductor processes with high process integration and fewer process steps along with reduced cost.

In one aspect of the embodiments, a light-erasable embedded memory device is provided consisting of a substrate with a memory region and a core circuit region, a floating gate on the memory region of the substrate, at least two light-absorbing films above the floating gate, wherein each light-absorbing film is provided with at least one dummy via hole overlapping the floating gate, and a dielectric layer on each light-absorbing film and filling up the dummy via holes.

In another aspect of the embodiments, a method of manufacturing a light-erasable embedded memory device is provided. The method includes the steps of providing a substrate with a memory region and a core circuit region, forming a floating gate on the memory region, forming at least two light-absorbing films above the floating gate over the memory region and the core circuit region, performing an etch process on each light-absorbing films to concurrently form at least one dummy via hole and via holes in each light-absorbing film respectively above the memory region and the core circuit region, wherein the dummy via holes overlap the floating gate, and forming a dielectric layer over each light-absorbing film and filling up the dummy via holes and the via holes.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Features will become apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which:

FIG. 1 is a cross-sectional view of a conventional single poly non-volatile memory device;

FIG. 2 illustrates a cross-sectional view of the light-erasable embedded memory device and MOS transistors respectively in a memory region and a core circuit region after front end of line (FEOL) stage according to one embodiment of the present invention;

FIG. 3 illustrates a cross-sectional view of the light-erasable embedded memory device and MOS transistors respectively in a memory region and a core circuit region in the back end of line (BEOL) stage according to one embodiment of the present invention;

FIG. 4 illustrates a cross-sectional view of the light-erasable embedded memory device and MOS transistors respectively in a memory region and a core circuit region after the back end of line (BEOL) stage according to one embodiment of the present invention;

FIG. 5 illustrates a schematic top view of the light-absorbing film with a pattern of dummy via holes according to one embodiment of the present invention;

FIGS. 6A-6D are top views schematically showing several exemplary patterns of how the dummy via holes are distributed above the floating gate;

FIGS. 7-10 are cross-sectional views illustrating a manufacturing flow of an illuminating efficiency-increasable and light-erasable embedded memory device according to an embodiment of the present invention; and

FIG. 11 illustrates a cross-sectional view showing the UV light passing through the dummy via holes and reaching the floating gate according to one embodiment of the present invention.

DETAILED DESCRIPTION

Advantages and features of the embodiments may be understood more readily by reference to the following detailed description of preferred embodiments and the accompanying drawings. Embodiments may, however, be embodied in many different forms and should not be construed as being limited to those set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey exemplary implementations of embodiments to those skilled in the art, so embodiments will only be defined by the appended claims. Like reference numerals refer to like elements throughout the specification.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

It will be understood that when an element or layer is referred to as being “on”, “connected to” or “coupled to” another element or layer, it can be directly on, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on”, “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result of (for example) manufacturing techniques and/or tolerances are to be expected. Thus, these embodiments should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the embodiments. Note that the size, the thickness of films (layers), or regions in diagrams may be exaggerated for clarity.

Hereinafter, a method of manufacturing an illuminating efficiency-increasable and light-erasable embedded memory device according to an embodiment of the present invention will be described with reference to FIGS. 2 to 4, which are cross-sectional views taken along a line transversal across the patterns of gate electrodes in memory region and logic region. In FIGS. 2 to 4, some components are enlarged, reduced in size, or omitted for ease of understanding.

Refer to FIG. 2, which is a cross-sectional view of the memory devices and MOS transistors respectively in a memory region and a core circuit region after a front end of line (FEOL) stage according to one embodiment of the present invention. A substrate 200 is provided to serve as a base for forming the semiconductor devices. The substrate 200 includes a memory region 202 and a core circuit region 204, and a memory device 206 has been formed on the substrate 200 in the memory region 202. The substrate 200 may be a silicon substrate. The memory device 206 may be composed of two MOS transistors 208 and 210 disposed adjacently on the substrate 200, wherein the gates of the MOS transistors 208 and 210 are respectively used as a select gate 216 and a floating gate 218 of the memory device 206. MOS transistors 212 and 214 may be further formed on the substrate 200 in the core circuit region 204. The materials and methods for forming these various components of the memory device 206 and of the MOS transistors 212, 214 are well-known to those having ordinary knowledge in the art, and therefore no further description will be provided herein.

An interlayer dielectric (ILD) 220 is formed on the substrate 200 and covers the memory device 206 and the MOS transistors 212 and 214. The material of the interlayer dielectric 220 may be silicon dioxide or silicon nitride, and the formation method of the dielectric layer 220 may be chemical vapor deposition (CVD).

Thereafter, a contact plug 222 is formed in the dielectric layer 220. The material of the contact plug 222 may be a metal such as tungsten. The contact plug 222 may be formed by patterning the dielectric layer 220 to form a plurality of openings 224 in the dielectric layer 220, and then performing a gap filling process to fill conductive materials into the openings 224. An additional contact etch stop film (not shown) may be formed conformally on the MOS transistor 208, 210 and the substrate 200 by SACVD.

Next, refer to FIG. 3, which is a cross-sectional view of the light-erasable embedded memory device and MOS transistors respectively in a memory region and a core circuit region in a back end of line (BEOL) stage according to one embodiment of the present invention. A light absorbing film 225 is first formed on the dielectric layer 220 to prevent the UV light from being reflected. The light absorbing film 225 may be formed of silicon oxynitride (SiON) material with a thickness of about 400 Å (angstrom) by PECVD. A dielectric layer 226 is formed on the light absorbing film 225. The material of the dielectric layer 226 may be silicon oxide or low-K fluorosilicate glass (FSG) with a thickness of about 5000 Å, and the formation method of the dielectric layer 226 may be CVD.

A metal layer 228 is formed in the dielectric layer 226 and through the light absorbing film 225, and the metal layer 228 may be used as a metal interconnect structure. The material of the metal layer 228 may be copper, and the metal layer 228 may be formed through a metal damascene process.

Next, a cap film 230 is formed on the dielectric layer 226. The material of the cap film 230 may be silicon nitride; more specifically, UV-transparent silicon nitride (UV-SiN) with a thickness of about 700 Å. The formation method of the cap film 230 may be CVD.

The foregoing steps for forming the dielectric layer 226, the metal layer 228, and the cap film 230 are repeated at least several times depending on the number of the metal layers. In the present embodiment, these steps are repeated five times; however, the number of times and the thicknesses of the three layers may be changed according to the design of the metal interconnect structure by those having ordinary knowledge in the art.

While repeating the steps of forming the dielectric layer 226, the metal layer 228, and the cap film 230, a fuse structure 232 may be formed in the dielectric layer 226 and through each cap film 230. The fuse structure 232 may be coupled to a doped region 234 of the MOS transistor 212 and a doped region 236 of the MOS transistor 214 via the contact plug 222. The material of the fuse structure 232 may be copper, and the fuse structure 232 may be formed through the metal damascene process. The fuse structure 232 can be adopted for repairing circuits by utilizing a laser beam to radiate the fuse structure 232. As such, there are no other metal layers above the fuse structure 232. Moreover, as the laser beam is employed for repairing the circuits, the opening is usually reserved on top of the fuse structure 232 in favor of repairing the circuits through the laser beam.

While repeatedly forming the dielectric layer 226, the metal layer 228, and the cap film 230, a conductive wire 238 may be formed in the dielectric layer 226 at the same time, and the conductive wire 238 may be respectively coupled to the doped regions 240, 242 and the select gate 216 of the memory device 206 via the contact plug 222. The material of the conductive wire 238 may be copper, and the conductive wire 238 may be formed through the metal damascene process.

In the level with an ultra-thick metal layer 228 (e.g. with a thickness of 35K Å), such as M7 and M8 shown in FIG. 1, the size of the metal layer (pattern) 228 is so large that high energy exposure is required in the photolithographic process to properly define the metal pattern. With such high energy exposure, the incident light is much easier to be reflected by the underlying layers, such as the light-reflecting metal layer directly below (i.e. the metal layer in M6) under the condition that adjacent layers are not particularly light-absorbing. The reflected light would cause an abnormal exposure and change the dimension of the metal layer, which is referred herein as a necking issue.

In order to solve this issue, the conventional structure shown in FIG. 1 illustrates that M7 and M8 levels with ultra-thick metal layer 228 are particularly provided with an intermediate light-absorbing film 239 amid the dielectric layer 226—more specifically, in the bottom level of the ultra-thick metal layer 228—to absorb the incident light and/or the reflected light. The material of the light-absorbing film 239 may be silicon oxynitride (SiON) with a thickness of about 900 Å. The formation method of the light-absorbing film 239 may be CVD. Via the light-absorbing film 239, a portion of the high energy incident light will be absorbed thereby making the underlying layer less reflective.

Next, refer to FIG. 4, which is a cross-sectional view of the light-erasable embedded memory device and MOS transistors respectively in a memory region and a core circuit region after the back end of line (BEOL) stage according to one embodiment of the present invention. A thick dielectric layer 244 is formed on the cap film 230. The material of the dielectric layer 244 may be silicon oxide with a thickness of about 12K Å, and the formation method of the dielectric layer 244 may be CVD.

Thereafter, a pad 246 is formed in the dielectric layer 244, and the pad 246 is coupled to the metal layer 228 in the M8 level. The material of the pad 246 may be aluminum (Al), and the pad 246 may be formed through forming an opening 248 in the dielectric layer 244 and forming a pad material layer on the dielectric layer 244 to fill the opening 248. After that, a photolithography process and an etching process are performed to define the pad 246. In another embodiment, the pad 246 may also be constructed by performing the metal damascene process.

Afterwards, a dielectric layer 250 is formed on the dielectric layer 244 and covers the pad 246. The material of the dielectric layer 250 may be phosphosilicate glass (PSG) with a thickness of about 4K Å, and the dielectric layer 250 may be formed by CVD.

Next, a passivation layer 252 is formed on the dielectric layer 250. The material of the passivation layer 252 may be silicon nitride with a thickness of about 5K Å, and the formation method of the passivation layer 252 may be CVD.

In the present embodiment, the metal interconnect structure 254 may be composed of the dielectric layer 220, the contact plug 222, a layer stack including the plurality of dielectric layers 226, the metal layers 228 and the cap films 230, and the fuse structure 232, the conductive wire 238, the dielectric layer 244, the pad 246, the dielectric layer 250, and the passivation layer 252, for example.

In addition, an opening 258 may be formed in the dielectric layer 250 and the passivation layer 252 above the pad 246 of the metal interconnect structure 254. The opening 258 exposes the pad 246, such that the pad 246 can be coupled to external conductive wires (not shown). Furthermore, an opening 260 may be formed in the dielectric layer 250 and the passivation layer 252 directly above the region of the floating gate 210. The opening 260 is prepared for UV erasure. By removing a portion of the top dielectric layer 250 and the passivation layer 252, the UV light will more readily reach the floating gate 210 and achieve the erase actions.

As shown in FIG. 4, however, the two thick light-absorbing films 239 (e.g. with a total thickness over 2000 Å) amid the (ultra-thick metal) UTM level of the layer stack which are for solving the necking issue may completely obstruct the incident UV light, thereby causing the data erase process to fail.

In order to solve this problem, the present invention provides a novel layer structure and a method which may facilitate the data erase process in the floating gate while still preventing the conventional UTM necking issue. Refer to FIG. 5, which is a top view of the light-absorbing film 239 shown in FIG. 4. The solution to the UV erase fail issue is to form multiple dummy via holes 264 in the light-absorbing films 239 directly above the floating gate 210 in the memory region 202. Each dummy via hole 264 allows the incident UV light to pass through without being absorbed or blocked by the light-absorbing films 239. The dummy via holes 239 shown in FIG. 4 are formed in array order. This may enable the UV light to be uniformly spread on the floating gate region. In the embodiment of the present invention, the dummy via holes 264 may be formed in the light-absorbing film 239 of the M7 or M8 level, both levels, or even the Ml level, depending on the process requirements.

The dummy via holes 264 may be distributed above the region of the floating gate 210 in different patterns. FIGS. 6A-6D show several exemplary patterns of how the dummy via holes are distributed above the floating gate 210. In FIG. 6A, the dummy via hole 264 is one large rectangular opening spreading over all floating gates 210 in the region, including adjacent select gates 208 and the active areas 266 formed below. In FIG. 6B, the dummy via holes 264 are uniformly distributed in array order over the floating gates 210 in the region. In FIG. 6C, the dummy via holes 264 are only spread above two ends of the floating gates 210. The dummy via holes 264 are rectangular patterns spreading and extending between opposite ends of two adjacent floating gates 210. In FIG. 6D, the dummy via holes 264 are cross patterns distributed only above two ends of the floating gates 210. The principle of the present invention is to form dummy via holes 264 above the floating gates, either partially overlaying or entirely overlaying them, as long as the UV light may reach the gate region to fulfill the purpose of data erasure.

The process of forming the dummy via holes 264 amid the dielectric layer 226 will be explicitly described with reference to FIGS. 7-10. Please note that FIGS. 7-10 mainly illustrate the structure of the UTM level (e.g. M7 and M8) in which the dummy via holes are formed. The structures of other metal levels are omitted in the figures for simplicity of description. The process flow starts from a layer stack including the dielectric layer 226 and a M6 metal layer 228 formed within, a cap film 230 over the dielectric layer 226, a dielectric layer 226 a on the cap film 230, and a light absorbing film 239 on the dielectric layer 226 a. The substrate is divided into the memory region 202 with the floating gate 210 form thereon and the core circuit region 204 where the ultra-thick metal will be formed in subsequent processes.

Next, refer to FIG. 8, which illustrates an etch process is performed with a patterned photoresist (not shown) as a mask to concurrently form the dummy via holes 264 and a via hole 267 respectively in the memory region 202 and the core circuit region 204. The dummy via holes 264 are formed to allow the passing of the UV light in the data erase process, and the via hole 267 will be filled with metal material to form the via of the UTM structure. The dummy via holes 264 are formed above and at least partially overlap the floating gate of the memory region 202, while the via hole 267 is formed above the metal line in the core circuit region 204. It should be noted that the formation of the dummy via holes 264 may be integrated into the process of common logic circuits without increasing the process time, manufacturing costs, or number of steps.

Next, refer to FIG. 9, in which a thick dielectric layer 226 b is formed on the light absorbing film 239. Please note that the dummy via holes 264 in the memory region 202 and the via hole 267 in the core circuit region 204 are filled up by dielectric layer 226 b. The dielectric layer 226 denoted in previous figures may be considered as a combination of the dielectric layer 226 a and the thick dielectric layer 226 b. The dielectric layer 226 b is a thick layer with a thickness of about 36K Å for the UTM structure.

Next, refer to FIG. 10. After the thick dielectric layer 226 b is formed, a recess 268 is formed in the thick dielectric layer 226 b above the core circuit region 204. The recess 268 may be formed by using a photolithographic process and an etch process to define the UTM pattern. It should be noted that the etch process also removes a portion of the light absorbing film 239 and the underlying dielectric layer 226 a and cap film 230. Since the via hole 267 (FIG. 7) is formed before the etch process, the etch process would form an opening 270 in the dielectric layer 226 a and cap film 230 and expose the metal layer 228 below.

Last, as shown in FIG. 11, with the dummy via holes 264 formed in the light absorbing film 239 amid the thick dielectric layer 226 in the UTM level above the memory region 202, the UV light may reach the floating gate 218 and erase the stored data, while the UTM necking issue may still be prevented by the light absorbing film 239 absorbing excess UV light.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A light-erasable embedded memory device, comprising: a substrate with a memory region and a core circuit region; a floating gate on said memory region of said substrate; at least two light-absorbing films above said floating gate over said memory region and said core circuit region, wherein each of said at least two light-absorbing films is provided with at least one dummy via hole overlapping said floating gate; and at least two dielectric layers, each of which is on each of said at least two light-absorbing films and filling up said at least one dummy via hole.
 2. The light-erasable embedded memory device of claim 1, wherein said at least one dummy via hole of one of said at least two light-absorbing films overlaps said at least one dummy via hole of other said at least two light-absorbing films.
 3. The light-erasable embedded memory device of claim 1, wherein said at least one dummy via hole comprises multiple dummy via holes arranged in an array.
 4. The light-erasable embedded memory device of claim 1, wherein the material of said at least two light-absorbing films is silicon oxynitride (SiON) or silicon nitride (SiN) with relatively low transmission coefficient for UV light.
 5. The light-erasable embedded memory device of claim 1, further comprising an ultra-thick metal on said core circuit region of said substrate, wherein said ultra-thick metal forms in one of said at least two light-absorbing films and in one of said at least two dielectric layers.
 6. The light-erasable embedded memory device of claim 1, wherein the material of one of said at least two dielectric layers is fluorosilicate glass (FSG).
 7. The light-erasable embedded memory device of claim 1, wherein said memory region is a one-time programming (OTP) region.
 8. A method of manufacturing a light-erasable embedded memory device, comprising the steps of: providing a substrate with a memory region and a core circuit region; forming a floating gate on said memory region of said substrate; forming at least two light-absorbing films above said floating gate over said memory region and said core circuit region; forming at least one dummy via hole and via holes concurrently in said at least two light-absorbing films respectively above said memory region and said core circuit region, wherein said at least one dummy via hole overlap said floating gate on said memory region; and forming at least two dielectric layers respectively over each of said at least two light-absorbing films and filling up said at least one dummy via hole and said via holes.
 9. The method of manufacturing a light-erasable embedded memory device of claim 8, wherein said at least one dummy via hole of one said at least two light-absorbing film overlaps said at least one dummy via hole of other said at least two light-absorbing films.
 10. The method of manufacturing a light-erasable embedded memory device of claim 8, further comprising a step of performing an etch process on said core circuit region to form a recess in said at least two light-absorbing films and said at least two dielectric layers.
 11. The method of manufacturing a light-erasable embedded memory device of claim 10, further comprising a step of filling up said recess in said at least two light-absorbing films and said at least two dielectric layers with metal material to form a metal layer.
 12. The method of manufacturing a light-erasable embedded memory device of claim 11, wherein said metal layer is an ultra-thick metal (UTM).
 13. The method of manufacturing a light-erasable embedded memory device of claim 8, further comprising a step of irradiating UV light passing through said at least one dummy via hole and reaching said floating gate to erase storage data.
 14. The method of manufacturing a light-erasable embedded memory device of claim 8, wherein said memory region is a one-time programming (OTP) region. 